An object of the present invention is a modular optoelectronic connector that can be used especially when high transmission bit rates are encountered. High bit rates of this kind are encountered for example in the field of telecommunications, especially for the interconnection of SDH type telephone exchanges. Each channel of an exchange of this kind must indeed give a bit rate of 622 Mbits. The expected developments are such that these bit rates must be raised to 2.5 Gbits and then 10 Gbits. High bit rates of this kind are furthermore being encountered in more limited spaces, as for example in computer local area networks or in aircraft. The bit rate requirements may then be also high owing to transmissions of image signals. Furthermore, inside one and the same piece of equipment, for example for the connection between several electronic racks in one and the same electronic cabinet, it may be planned to have very high bit rates.
To provide for the transmission of information of this kind without being hampered by problems of crosstalk or electromagnetic noise, it is preferred to use optical links. The invention pertains in fact to all optical links in which, ultimately, information has to be conveyed at a high information bit rate.
The preparation of information in electrical form and its transmission in optical form requires the making of optoelectronic couplers. In a first approach, devices have been developed in which an electronic card comprises an optoelectronic coupler of this kind. In this case, the electronic board can be accessed from outside by an optical connector. However, such an approach dictates the reservation of space on such an electronic board to make the electro-optical conversions. With a view to miniaturization, another approach is becoming prevalent. In this other approach, the coupler is an integral part of a connector. With this type of development, harnesses are appearing for example on the market. Harnesses of this kind comprise a cable and optoelectronic connectors at each of its ends. In a harness, the connectors are mounted on a cable. In the invention, it is thus planned, if necessary, to make harnesses of this kind. However, more generally in the invention, it is provided that the connectors may be distributed separately from the cables.
An optoelectronic connector according to the invention then comprises an electronic port linked to a coupler that is itself connected to an optical port. A cable to be connected to the optical port is an optical cable. At an another end of a link, a reverse conversion is done, and another connector is mounted. For the user, on either side of the cable, the links are electrical. The optoelectronic conversion is transparent to the user. The advantage of these approaches is of course a gain in space on the electrical cards which no longer has to incorporate a coupling function. Another advantage is simplicity of use. All that remains is a constraint relating to the electrical supply of the coupler but this is done through the electrical port.
An embodiment of this kind however has the drawback of being costly to manufacture. Indeed, the technologies implied in such a connector require strict compliance with various physical constraints. Thus, on the electrical port side, given the high information bit rates (for example in the range of several Gbits), it is necessary to act efficiently to counter radioelectrical noises. In the coupler, it is necessary to take account of the problems of thermal dissipation of the transducers used. Indeed, the known transducers, namely laser diodes, can consume up to 100 milliwatts per unit. The heat dissipation related to the working of the transducer prompts a heating of this transducer, resulting in a drift in its operating frequency.
Cost-related problems, for their part, lead to the making of multifiber sets. Indeed, since the mounting of a connector for a single optical fiber is costly, the cost is substantially reduced by providing for the connections of bundles of optical fibers. For example, there are known embodiments in which twenty optical fibers are connected to a connector. However, while an embodiment of this kind leads to a reduction in the cost price per optical fiber of the connector, it does not accurately correspond to requirements. With embodiments of this kind, the user may have access either to a connector with very many optical fibers or to a connector with a single optical fiber. However the cost is high in both cases. In the invention, optoelectronic links are sought wherein it is possible to make use of a modularity: the user, as required, can associate a desired number of optical fibers to meet his requirements.
The making of multifiber sets furthermore leads to specific difficulties. Indeed, owing to heat consumption, laser diodes have to be separated from one another by a substantial space inside the connector. Similarly, when the optoelectronic connector is mounted on an electronic card, the laser diodes are spaced out so that, they can be mounted therein. Besides, in order to be able to get connected to this type of connector, it is necessary to get close to a termination of an optical fiber of the optical radiating element of the coupler. Now, the multifiber optical connectors have a standardized distribution of the optical terminations. In this standardized distribution, the terminations are close to each other. It is then necessary to create a waveguide in the optoelectronic, connectors. This waveguide enables a geometrical matching between the necessarily big spacing between the laser diodes mounted in the optoelectronic connector and a close spacing close of the terminations of the optical fibers presented in a standardized optical connector. The making of a waveguide of this kind complicates the coupler. This waveguide itself must also comply with the above-mentioned constraints.
In practice, to make optoelectronic connectors of this kind, laser diodes using Vcsel technology are used. The term Vcsel refers to vertical cavity solid emitting lasers. With vertical cavity solid emitting lasers of this kind, the laser radiation is actually scattered in a scattering cone whose angular aperture is about 8xc2x0 C. to 12xc2x0 C. It becomes easier to place an optical fiber termination in front of a cone of this kind to pick up the optical signal sent. However, the presence of the waveguide mentioned here above implies the making of two optical interfaces. A first interface is located between the laser diode and the input of the waveguide. A second interface is located at the output of the waveguide and at the input of the optical connector. These two interfaces lead to insertion losses which are themselves curbed by improving the quality of the optical terminations of the fibers of the optical connector and/or of the waveguides. For example, these ends of the fibers are polished by means of a plane or spherical polishing. If the polishing is plane, preferably it is slightly inclined with respect to the incident direction of the optical transmission so as not to prompt any parasitic reflections, both on the side of the Interface with the laser diode and on the side of the interface with the optical connector. Ultimately, the presence of this waveguide results in a complex and costly structure if it is sought to prevent ft from being a generator of transmission losses.
Furthermore, the electrical port that conveys the data elements must be especially well protected to prevent electromagnetic parasites. This shielding may be conventionally obtained by arrangements of metal partition walls. However, this type of approach is not compatible with desired goals of miniaturization and modularity of an optoelectronic connector. Or else, the manufacturing equipment becomes so precise that handling it runs counter to the conditions of very large-scale production.
In short, the approaches used for the prior art optoelectronic connectors are costly, not modular and do not have as good a transmission quality as would be desired.
It is an object of the invention to overcome these drawbacks by proposing an approach to the integration of the laser diodes into the optoelectronic connector that resolves all these problems simultaneously. According to a first embodiment of the invention, laser diodes are made by means of a weakly dissipative gallium arsenide (GaAs) technology. Using a thin layer transfer technique, these laser diodes are then placed directly on an integrated circuit comprising circuits for the driving, supply and amplification of the signals converted by the laser diodes. This direct transfer makes it possible to overcome the need for a printed circuit or a hybrid circuit which, in the prior art, enables the association of the laser diodes and the various electronic circuits needed to make them work.
This integrated circuit is itself directly placed in a package of the optoelectronic connector without being placed in an intermediate package that would contain it. Contact pads of this integrated circuit are connected to metallized zones made in a cavity of this package. Other pins of this integrated circuit are also connected to contact pads of one or more laser diodes transfer on this integrated circuit. These connections are made by wire bonding type microconnection techniques, ball grid array type or BGA type arrangements, or anisotropic type films. The package thus made is then sufficiently thin to be capable of being stacked at will and to enable the constitution of modular optoelectronic connectors with a number of electrical and/or optical ports that is determined at will.
Furthermore, the fact of transfering laser diodes, especially gallium arsenide laser diodes, on an integrated circuit that comprises all the functions needed for these diodes, enables them to be placed therein with a mutual spacing such that it is equal to the spacing with which the terminations of the optical fibers are presented in the standardized optical connector. By acting in this way, direct compatibility is then achieved with a standardized distribution of an optical connector. Thus, it becomes unnecessary to interpose an optical waveguide between the optoelectronic coupler and the optical port. Consequently, insertion losses in the optical fibers are smaller. Consequently, the care taken in the making of the optical connectors becomes less important while at the same time providing for greater efficiency. Naturally, the cost of the connector is reduced owing to the absence of this interposed waveguide.
The solution to the problems of shielding is then preferably obtained by making a package of the connector by means of MID technology. With a technology of this kind, it is possible in one pass to metallize a part of a structure, a package, made of plastic or any other material. In the invention, in this structure, mechanical receptacles are made designed to receive male or female contacts of the electrical port. These receptacles have for example the shape of a cylindrical tube. Through their metallized back, they are connected to a contact that is introduced therein. Furthermore, the external surface of these tubes is metallized and this external metallization is connected to a ground contact. The external metallization is used as a shielding. If need be, the rest of the structure is molded on this assembly. By acting in this way, with metallizations made in one or two passes, the need for handling the partition walls is removed. The method can easily be adapted to large-scale manufacture because the structures are preferably molded.
An object of the invention therefore is an optoelectronic connector comprising a package, an optical port, an electrical port, an optoelectronic circuit positioned in this package and connected to these two ports, characterized in that the optoelectronic circuit comprises a bare control and emission-detection integrated circuit chip, an internal wall of the package being provided with metallized connections, pads of this integrated circuit being connected directly to the metallized connections, laser diodes being transferred on the integrated circuit.
This connector is thus constituting a basic unit link. By juxtaposing such basic unit links, it is possible to simply and efficiently make multiple-channel links. Thus, it is possible to set up a modular assembly of n links at very high bit rate or again a very high bit rate link obtained by the multiplexing of n links at a lower bit rate.